Build Mono WebAssembly runtime and BCLs

We force using Emscripten 1.38.47 as there is a regression in 1.38.48
and 1.39.x which makes the generation of our .wasm file fail.

Up until now we used the desktop BCL (compiled with desktop Mono)
for both desktop and Android, but that does not work for WebAssembly
(and we suspect Android issues related to it).

So we now build the Android and WebAssembly BCLs in the relevant
containers, which are later copied in the templates directory to
include on export. We already have the desktop BCL from the regular
build.

Dockerfile.javascript

@@ -1,12 +1,29 @@
-FROM godot-fedora:latest
+ARG mono_version
+FROM godot-mono:${mono_version}
+ARG mono_version
 
 RUN dnf -y install --setopt=install_weak_deps=False \
       java-openjdk yasm && \
     dnf clean all && \
     git clone https://github.com/emscripten-core/emsdk && \
     cd emsdk && \
-    ./emsdk install 1.39.0 && \
-    ./emsdk activate 1.39.0 && \
+    ./emsdk install 1.38.47-upstream && \
+    ./emsdk activate 1.38.47-upstream && \
     echo "source /root/emsdk/emsdk_env.sh" >> /root/.bashrc
 
+RUN git clone https://github.com/mono/mono --branch mono-${mono_version} --single-branch && \
+    cd mono && git submodule update --init && cd .. && \
+    export MONO_SOURCE_ROOT=/root/mono && \
+    git clone https://github.com/godotengine/godot-mono-builds && \
+    cd godot-mono-builds && \
+    git checkout bd129da22b8b9c96f3e8b07af348cc5fb61504bf && \
+    python3 patch_emscripten.py && \
+    python3 wasm.py configure --target=runtime && \
+    python3 wasm.py make --target=runtime && \
+    cd /root/mono && git clean -fdx && NOCONFIGURE=1 ./autogen.sh && \
+    cd /root/godot-mono-builds && \
+    python3 bcl.py make --product wasm && \
+    cd .. && \
+    rm -rf /root/mono /root/godot-mono-builds
+
 CMD ['/bin/bash']